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New Scientist Live

Orang-utans fashion only known animal instrument

Video: See the virtuoso leaf players

By Ewen Callaway

As wind instruments go, folded vegetation seems a little on the primitive side. Orang-utans have been found to blow through leaves to modulate the sound of their alarm calls, making them the only animal apart from humans known to use tools to manipulate sound.

The orang-utan’s music, if you can call it that, is actually an alarm call known as a “kiss squeak”.

“When you’re walking the forest and you meet an orang-utan that not habituated to humans, they’ll start giving kiss squeaks and breaking branches,” says Madeleine Hardus, a primatologist at the University of Utrecht in the Netherlands, who documented the practice among wild apes in Indonesian Borneo.

She contends that orang-utans use leaves to make kiss squeaks to deceive predators, such as leopards, snakes and tigers, as to their actual size – a deeper call indicating a larger animal.

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Baritone squeaks

Orang-utans also produce kiss squeaks with their lips alone or with their hands. To determine if the leaves make a difference, Hardus’s team recorded a total of 813 calls produced by nine apes, and then measured the pitch of the different kinds of kiss squeaks made by each animal.

Across all nine orang-utans, the unaided kiss squeaks came out with the highest pitch, followed by calls produced when the apes put their hands over their mouths. But leaves lowered the high-pitched calls the most, Hardus’ team found.

What’s more, the orang-utans that were unaccustomed to Hardus’ team produced leaf calls at far higher rates than apes that were used to humans.

“It looks like orang-utans try to deceive the predator when using the kiss squeaks on leaves, because orang-utans only use it when they’re highly distressed,” she says.

Understanding others

“An orang-utan would have to understand how their calls are being perceived by other animals, a clear example of theory of mind,” says Robert Shumaker, an orang-utan expert at the Great Ape Trust of Iowa, in Des Moines. “If, in fact, this is what they’re doing, deception is a perfectly plausible possibility.”

“It’s a particularly interesting form of tool use, to me, because it gets away from a lot of the typical examples of foraging,” Shumaker adds. “It’s really, really nice to see an example that has absolutely nothing to do with food.”